الفهرس 
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Abstract
A log-periodic antenna is a main type of frequency independent antennas, that remains its electrical. properties (directional1ty, input impedance and polarization) constant within a very > , . wide frepenoy range, up to 20:1 and even 30:1. The main properties of this antenna is that, the directional pattern has no sldelobes and it can be easily fed.
The present work contt:fins two proposed theoretical trea1ments of L PDA. The first method is based on the determination of the total reflections, at any point t:flong the periodic structure, by summing up the reflections caused by different sections, assuming that the reflection coefficients at the dipole elements snall so that higher order multiple reflections are neglected. This method is long but straight forward and’ it contains no advanced mathEmatics. The second method is based on Hill’s equation and Floquet’s method of BnBlysis. This method has no restriction on the values of the reflection coefficients at the dipole elElllents t:fnd thus it gives good qualitative as well as quantitative results. Numerical computations for the various characteristics of
L PDA are carried out using this second method, and the results
1 Bre in good agreement lIith previous authors experimental and theoretical results • br>The thesis is divided into three main chapters. The first chapter covers a lmost all previous studies of log periodic brantennas.. This chapter is divided into five sections. In the first section, the structure and geometry of L P antennas are treated.. The second section, gives the modified versions of L PDA, especially the helical log .... periodie array, which overcomes large size in the transverse direction.. Different methods of feeding L P structures (balanced or unbalanoed) with special attention to the feeding method using ’W8veguides and the feeding method using strip lines are discussed in the third section.. The fourth section gives the desi:gn of L PDA and helical L P A .• Previous theoretical studies of L PDA are carried out in seetion five .. br>The second chapter is devoted to the proposed theoretical analysis, while third chapter is devoted to the experimental investigations, the conclusion and appendices composing the proofs of some equations appearing throughout the manuscript .